There is high variability of anti-parkinsonian prescribing patterns across physicians, and across countries, without any standard practice. Some hold off on levodopa (and start with dopamine agonsists) due to levodopa-induced-dyskinesias. Some like to use dopamine agonists in general, while others do not - perhaps due to some of the compulsive behavior type side effects (gambling, OCD, hypersexuality, etc...) . Some use rasagaline (Azilect), others do not.
In Europe in 2007, pramipexole was more popular (by sales $) than ropinirole. In US inpatients, use now about equal. Nobody really uses apomorphine, since it required injection (and used mostly for off / freezing episodes). Now have Cynapsus' sublingual apomorphine in trials, and will be used more for freezing episodes. Perhaps some might try to use it like a pill, but I think probably not, since it has a relatively short half-life.
Not sure about all the nuances about the differences in dopamine agonists. Some activate dopamine D2, D3, and other subtypes in different proportions / affinities. Here's a review of dopamine receptor subtypes and dopamine agonists:
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